The popularity of refillable containers has increased as the costs, both social and financial, associated with disposal of packaging have become less acceptable. For example, in many countries, water and other beverages are sold in refillable bottles. These bottles are often made from a type of plastic known as polyethylene terephthalate.
After use, refillable containers are returned to a bottling plant where they are cleaned and inspected before being refilled. This inspection, in addition to checking for physical damage such as cracks, screens the containers to eliminate those that include contaminants that might degrade the flavor, safety, or other qualities of the product that they are to contain. The risk of contamination is greater when a container is made from plastic, as opposed to glass, because some contaminants can be absorbed into the plastic walls of the container. Absorbed contaminants can persist despite cleaning procedures, and can later leach into the product.
High speed chemical detection equipment for analyzing vapors given off by residues in containers to determine the chemical composition of the residues has become available at reasonable cost. This equipment, which enables detection of residues in a container without slowing down the container as the container moves along a conveyor line, has proven to be particularly useful in systems for removing from the conveyor line containers that have been identified as potentially being contaminated.
Chemical detection equipment has been applied in detecting contaminants in refillable, reusable plastic bottles as the bottles move along a high speed conveyor line so that contaminated bottles can be rejected from the conveyor line. An example of such equipment is set forth in U.S. Pat. No. 5,318,911, entitled "System for Sampling and Determining the Presence of Compounds in Containers", which is incorporated herein by reference. U.S. Pat. No. 5,318,911 discloses a sampling head with one tube blowing gas into the open top of a bottle and an adjacent tube sucking air from the interior of the bottle to obtain a sample. The sample is then analyzed using a chemiluminescence technique to detect contaminants as indicated, for example, by the presence of nitrogen compounds in the sample. Other techniques and issues related to detecting contaminants in moving containers are discussed in U.S. Pat. Nos. 5,569,606, entitled "Method and System for Sampling and Determining the Presence of Contaminants in Recyclable Plastic Materials"; 5,567,623, entitled "Method and System for Sampling and Determining the Presence of Compounds"; 5,561,068, entitled "Method and System for Sampling and Determining the Presence of Compounds"; 5,536,935, entitled "Detection of Foaming Contaminants in Containers Using Image Processing"; 5,528,036, entitled "Spectral Detection of Contaminants in Containers"; 5,510,620, entitled "Detection of Turbid or Foaming Contaminants in Containers"; 5,486,693, entitled "Detection of Turbid Contaminants in Containers by Detecting Scattered Radiant Energy"; 5,472,882, entitled "Method and System for Sampling and Determining the Presence of Salts of Ammonia and Amines in Containers"; 5,470,754, entitled "Method and System for Sampling and Determining the Presence of Compounds"; 5,435,198, entitled "System for Sampling and Determining the Presence of Salts of Ammonia and Amines in Containers"; 5,418,170, entitled "Method and System for Sampling and Determining the Presence of Salts of Ammonia and Amines in Containers"; 5,397,540, entitled "System for Injecting Fluid into Spaced Containers Moving at Variable Speeds"; 5,388,705, entitled "Rejector System for Conveyor Line"; 5,376,550, entitled "Method and System for Sampling and Determining the Presence of Compounds in Containers"; and 5,352,611, entitled "Method and System for Sampling and Determining the Presence of Compounds in Containers", all of which are incorporated by reference. Many of these techniques are implemented by the ALEXUS inspection system available from Thermedics Detection, Inc. of Chelmsford, Mass.